It is well known that the speed and power output capabilities of a variety of semiconductor devices are dependent upon the carrier mobility and transit time response of these devices. It is further well known that these latter characteristics are temperature dependent. Thus, when these devices are driven beyond their upper power limits or current ratings, they may heat up to in turn reduce the levels of carrier mobility and transit time therein and thereby cause a concurrent reduction in speed and power output of these devices, and in some cases device burn-out. Thus, when these devices are mounted on lead frames or headers and encapsulated in a package, good heat transfer and heat dissipation from these devices have always been primary considerations in package design.
In the past, the use of passive cooling methods having good heat transfer characteristics and thermal dissipation characteristics for lead frames, component headers and the like has frequently been adequate for providing satisfactory heat dissipation and heat transfer for electronic devices operating within certain prescribed and normal limits of power output and operational speed. However, with the recent rapid advances in the art of integrated circuit memories, for example, where several thousand transistors may be fabricated in a single semiconductor chip, there is a definite need to provide an active enhanced cooling capability for these devices in addition to the above types of passive cooling methods.
Thus, active cooling structures may be used to provide an additional kind and degree of cooling for these semiconductor devices. This enhanced cooling may be desirable, for example, to allow these semiconductor devices to operate at even greater speeds and higher powers (and higher speed-power-product figures of merit) than were heretofore possible. These devices not only include integrated circuits as indicated above having many thousands of transistors therein, but they may also include individual power transistors which, with the help of additional active cooling, would be capable of operating at significantly greater speeds and output powers than they are presently capable of operating using only passive cooling methods.
The specific type of cooling employed herein and the technical field of the present invention is that of Peltier cooling capable of using either metal-metal or metal-semiconductor Peltier junctions. These junctions produce either a cooling or heating effect at the metal-metal or metal-semiconductor interface, depending upon the direction of current flowing across this interface. More specifically, there is either an evolution or absorption of heat at the Peltier junction depending upon the direction of current flowing thereacross. This effect has been described in many prior art patents and publications and is based upon a discovery made by Jean Peltier in 1834.
Circuits using Peltier junctions have also been described in the prior art, and one such circuit is described for example in U.S. Pat. No. 4,685,081 issued to Jay L. Richman and incorporated herein by reference. The Richman circuit is used for the thermal control of a bubble memory device, and in significant contrast to the invention described below, the Richman circuit uses Peltier cooling junctions which are positioned outside the heat sink and semiconductor device package in which the cooled semiconductor device is mounted. This type of Peltier junction mounting arrangement is inefficient in its cooling because of its physical separation from the semiconductor device being cooled and further because it is not integrally formed with heat sink support members for the semiconductor device being cooled.